Electrolocation? The evidence for redox‐mediated taxis in Shewanella oneidensis

Abstract

Shewanella oneidensis is a dissimilatory metal reducing bacterium and model for extracellular electron transfer (EET), a respiratory mechanism in which electrons are transferred out of the cell. In the last 10 years, migration to insoluble electron acceptors for EET has been shown to be nonrandom and tactic, seemingly in the absence of molecular or energy gradients that typically allow for taxis. As the ability to sense, locate, and respire electrodes has applications in bioelectrochemical technology, a better understanding of taxis in S. oneidensis is needed. While the EET conduits of S. oneidensis have been studied extensively, its taxis pathways and their interplay with EET are not yet understood, making investigation into taxis phenomena nontrivial. Since S. oneidensis is a member of an EET‐encoding clade, the genetic circuitry of taxis to insoluble acceptors may be conserved. We performed a bioinformatic analysis of Shewanella genomes to identify S. oneidensis chemotaxis orthologs conserved in the genus. In addition to the previously reported core chemotaxis gene cluster, we identify several other conserved proteins in the taxis signaling pathway. We present the current evidence for the two proposed models of EET taxis, “electrokinesis” and flavin‐mediated taxis, and highlight key areas in need of further investigation.

Solution‐Deposited and Patternable Conductive Polymer Thin‐Film Electrodes for Microbial Bioelectronics

“…This is the first example to demonstrate the deposition of two different microbial strains at distinct regions on the same substrate. Our approach takes advantage of insoluble electron acceptor taxis [ 67 ] or the electromigration of S. oneidensis toward the positive electrode during deposition. [ 69 ] By applying a positive potential and introducing a specific strain of S. oneidensis , we can deposit the microbes only on a desired region of the electrode surface.…”

“…Representative examples of 2D and 3D electrode interface layers designed to increase current densities are listed in Table 1. [56][57][58][59][60][61][62][63][64][65][66][67] Although 2D electrode interface layers in MESs usually generate lower absolute biotic current density compared with their 3D counterparts, we found that the improvement of current density using our PEDOT:PSS/PHEA-coated electrode surpassed that of other 2D and 3D interfaces. For example, a 2018 study reported that the steady-state current density increased a factor of 20 using a PEDOT:PSS-based, multilayer biocomposite interface layer.…”

Plasmonic Probing Single-Cell Bio-Current Waves with a Shrinking Magnetite Nanoprobe

“…We use a qualitative assay method to study the long-term EET process to prove this. The oscillation frequency of motile cells infers the rotation of the flagellar motor, which is associated with the proton motive force built by EET. − This phenomenon is described as EET-dependent electrokinesis. Here we measure the real-time plasmonic amplitude of a single MR-1@MNP cell during a 400 min EET process.…”

Electrochemical Microwell Plate to Study Electroactive Microorganisms in Parallel and Real-Time

“…Therefore, it produces conductive appendages being extensions of the outer cell membrane ( Subramanian et al, 2018 ). Thus, if no mediator is present EET is only possible, if the suspended cells have at least temporary physical contact with the anode ( Harrisa et al, 2010 ; Starwalt-Lee et al, 2021 ). This limitation and the insufficient mediator production are the main reasons that S. oneidensis cannot reach high current densities ( Logan et al, 2019 ).…”